Single-modulator and two-modulator sequential color display systems have been used as a cost effective alternative to three-modulator full color display systems. Such systems are described in published European Patent Application EP1,098,536 A2, to Duane Scott Dewald, which is hereby incorporated by reference.
As shown in FIG. 1, the brightness of the single-modulator 10 and two-modulator 25 sequential color display systems is improved through the use of a recycling solid light pipe 5 (or recycling light tunnel) coupled with a dynamic filter 7 and 14, which provides one or more segments of each primary color filter to the light beam at all times. As shown in FIGS. 1C-1E, the recycling pipe 5 consists of a light pipe 5b and a reflective plate 5a with an aperture 50a The exit aperture of the recycling pipe 5 typically has the same cross section aspect ratio as that of the modulator 9, 16 and 17 used by the display systems 10 and 25.
In FIGS. 1A-1B, the input light 3 and 13a is focused into the entrance aperture of a recycling pipe 5 through an aperture 50a in a reflective plate 5a. Light beams 6 and 13b exit recycling pipe 5 more uniform and homogeneous and impinge on the color wheels 7 and 14 (i.e., dynamic filter). Some of the light beam impinging on the color wheels 7 and 14 passes through each of the three or more color segments illuminated by the beam. Each segment transmits some of the incident light and reflects the remainder, which reenters the recycling pipe 5 and travels toward the reflective plate Sa. Some of this light impinges on the reflective plate 5a and gets reflected back toward the color wheels 7 and 14 and the rest of it passes through the aperture 50a toward the lamp reflector 2 and 12. Lens 8 focuses light transmitted by the color wheel 7 onto the spatial light modulator 9 as shown in FIG. 1A.
As shown in FIG. 1B, light beam 13c exiting the color wheel 14 enters a TIR (total internal reflection) prism assembly 15 which reflects the light beam to a color splitting prism assembly 18. As a result, modulator 17 is always completely illuminated by one primary color (e.g., red), while the other two primary colors (e.g., blue and green) scroll across modulator 16. The modulated light is focused by projection lens 19 onto a screen 20 to form an image.
Known single-modulator and two-modulator sequential color display systems suffer from low efficiency and lack of compactness. Therefore, there is a need for compact, light-weight, more efficient and cost-effective illumination systems to provide uniform light distribution over a certain area such as the active area of a modulator in sequential color display systems.